In the field of sol-gel coatings, those obtained from metal alkoxides based on silicon (silanes) or based on aluminum (aluminates) are known in particular.
These coatings are currently being widely developed in the field of cooking articles, and in particular as nonstick coatings covering the internal cooking surface.
These nonstick coatings, which are synthesized by sol-gel from metal polyalkoxylate precursors, have a hybrid network, generally of silica with grafted alkyl groups. By comparison with the traditional nonstick coatings for cooking articles based on polytetrafluoroethylene (PTFE), this type of coating obtained by sol-gel has, as the main advantage, very good performance at temperatures above 300° C.
A formulation of this type of coating is described in the international application WO 2008/010639. It is in particular to a coating formed by sol-gel from a silane-based composition, in which said coating is applied to an anodized aluminum substrate intended to be used as a cooking article.
In addition, the applicant has developed a coating of this type intended for cooking articles. Thus, the international application WO 2008/142327 and European application EP 2 139 964, belonging to the applicant, describe a coating formed by sol-gel from a composition based on at least one metal alkoxide and a colloidal metal oxide, in which a very small amount of silicone oil is added. The coating thus formed is not only resistant to high temperatures, but it is also capable of withstanding several minutes of exposure to the flame of a Bunsen burner (of which the temperature is above 600° C.) and then quickly recover its hydrophobic character.
International patent application WO 2007/104258 and European patent application EP 1 835 002 belonging to the CERASOL HONG KONG LTD company specializing in research and development of ceramic coatings for domestic and industrial applications, describes the formulation and process of production of a nonstick coating having improved abrasion resistance, hardness and durability with respect to a PTFE coating. It involves a two-layer coating consisting of a primer comprised of colloidal silica, organoalkoxysilanes optionally with a polydimethylsiloxane (PDMS), and a transparent finishing layer comprised of organoalkoxysilane colloidal silica including a fluoroalkoxysilane to provide the nonstick property and optionally a PDMS.
Finally, patent application CN 101502378 describes in detail the formulation of a coating for cooking articles making it possible to reduce and even eliminate the oxidation of edible oils. It is a coating formed by sol-gel from a composition based on methyltrimethoxysilane (MTMS) or methyltriethoxysilane (MTES) and a colloidal alumina dispersion, filled with different inorganic fillers including a nano-silver powder enabling the oxidation mechanism of the oils to be stopped.
None of these sol-gel coatings known from the prior art is equipped with a functional indicator, i.e. an indicator enabling the user of the article, on which the coating in question is deposited, to be supported and guided.